The invention relates to a process for manufacturing granules containing sodium chlorite by drying an aqueous medium containing chlorite in a fluidized bed permanently containing seeds smaller in size than the required granules.
Technical literature contains references to various processes for preparing solid sodium chlorite from a solution or, generally, any chlorite containing aqueous medium. Crystallization is the first stage in one of these processes and this may be followed by centrifugal separation and drying of the crystals (see, for example, U.S. Pat. No. 2,520,915 of Apr. 26th, 1945, in the name of DIAMOND ALKALI CO). In another process, which has become a standard procedure, drying is effected by atomization (cf. the article by T. P. Forbath in Chemical Engineering, 1961, 68, No. 12, pps. 180-182), the end product being a fine crystalline powder. Rotary drum driers heated internally by steam tubes and supplied with product by a prethickener (cf. FIAT report, Final Report No. 825, chlorine dioxide and sodium chlorite at I. G. Farben, Griesheim, p. 4) are also used. Here, the end product is in flake or fine crystal form. Occasionally, the chlorite is dried in several stages at progressively increasing temperatures (cf. Belgian Pat. No. 452,924 of Oct. 22nd, 1943, in the name of Solvay & Cie). Manufacture of sodium chlorite granules in which the first stage is preparation of trihydrate crystals by evaporation under vacuum, then followed by fusing individual crystals and arranging them in the form of a fluidized bed in a solution saturated with chlorite, or even drying the surface of the trihydrate crystals with a stream of inert gas (French Pat. No. 1,187,352 of Nov. 29th, 1957, and French Pat. No. 1,228,234 of Mar. 10th, 1959, both in the name of SOCIETE D'ELECTROCHIMIE, D'ELECTROMETALLURGIE ET DES ACIERIES D'UGINE) has also been suggested. Lastly, there have been references to the fact that use of a fluidized bed process for drying trihydrate crystals is beneficial. (A. I. Kachalov -- Khimicheskaya Promyshlennosti, 1960, pp. 336 to 339).
Owing to the comparatively large number of chemical operations involved, most of these processes are extremely laborious. Finally, others such as the atomization or rotary drum processes produce chlorites in powder, fine crystal, or flake form which do not meet the criteria of many customers.